Light visible to human eyes may consist of light spectrums of seven colors upon superposition, and human visual perception to the same color is basically the same under different illuminations. For example, a white object may look like white in the morning light as the sun rises; and it may still look like white under the faint light at night. This is because human brains have been adapted to color rendition of an object under different lighting conditions.
However, a front end device of a video monitoring system, such as an analog camera, a network camera or a digital camera, may not have the adaptability of human eyes. Since light of different color temperatures may have different color components, in allusion to the same object, colors of an image captured by the front end device may likely be different under illumination by light of different color temperatures. Specifically, the front end device may capture an image for an object, which includes three color components, namely Component R (red), Component G (green) and Component B (blue). However, colors of the image finally obtained may likely appear not to be consistent as the object actually seems, due to impacts of the color of the object itself, color temperature of ambient light, and photosensitive properties of optical filters and sensors on various color components, etc. To ensure the colors of the image captured by the front end device furthest close to human visual perception, image processing such as white balance may be performed on the captured image.